1. Field of the Invention
The present invention generally relates to a display device, an image forming apparatus, a recording medium and a display method, and, in particular, to a display device employing light emitting diodes, an image forming apparatus using the display device, a recording medium storing a program for controlling the display device, and a display method of displaying using light emitting diodes.
2. Description of the Related Art
Recently, saving power of an image forming apparatus such as a copier, a printer, a facsimile machine or the like has been demanded strongly. In fact, even there is a standard in which a power consumption at a time of a standby mode is less than 10 W, and, also, each of a returning time required for returning from the standby mode to a normal mode and a shifting time required for changing from the normal mode to the standby mode is less than ten seconds.
In such a situation, a power saving method which has been employed in an image forming apparatus in the related art having an operation panel employing LEDs (light-emitting diodes), specifically, a power saving method in which almost all parts of the apparatus including the operation panel other than a partial circuit are disconnected from the power source, may cause inconvenience to a user. Accordingly, a new power saving method should be considered. In particular, when an arrangement is made such that shift from the normal mode to the standby mode is automatically performed quickly, the operation panel may be disconnected from the power source when a predetermined time has elapsed while no operation is performed by a user on the operation panel by some reason even during operation for changing an operation condition or the like of the apparatus. Thereby, display of the operation condition which is being set may be extinguished from the operation panel unexpectedly, or the operation condition itself may be erased unexpectedly. Thus, serious inconvenience on use may occur.
Further, although the LEDs on the operation panel are effective displaying measures for displaying operation states of respective parts in the image forming apparatus, a power saving method concerning driving of the LEDs is very important in the above-mentioned trend because the driving power consumption by the LEDs is very large.
There are two types of LED driving methods. One thereof is a static driving method in which an LED driving unit is provided for each LED. The other one is a dynamic driving method in which many LEDs arranged in a form of a matrix are driven by a time-division manner by a combination of a relatively small number of a common driver and a data driver. In a case of using many LEDs, the latter method is used in many cases.
Japanese Laid-Open Utility-Model Application No. 6-2391 discloses an LED driving circuit employing a power saving technique for the dynamic driving method. In this circuit, constant-current ICs are used as the above-mentioned data driver, and, as a power source for driving LEDs, a low-voltage power source is used in addition to a power source for driving a control circuit. That is, by using a low voltage for driving the LEDs, it is possible to reduce power consumption in the LED panel.
The above-described LED driving circuit disclosed by Japanese Laid-Open Utility-Model Application No. 6-2391 is suitable for a use in an arrangement having very many LEDs which are single color light emitting LEDs. However, as in an operation panel in an image forming apparatus, having a number of LEDs of total several tens or less, and, also, emitting a plurality of colors, a problem occurs. This is because, in such a case, a special power source only for driving the LEDs is needed although the number of the LEDs is small, and, also, different constant-current ICs are needed for LEDs emitting light of different colors. Further, at a time the image forming apparatus returns from the standby mode to the normal mode, there is a somewhat delay from a time a user operates the operation panel. Accordingly, it is necessary that there is a clear difference between the standby mode and normal mode in the operation panel easily noticeable by the user.
The present invention has been devised in consideration of the above-mentioned situations.
In a display device, according to the present invention, in which first and second driving parts are connected with in series so as drive in a time-division manner light-emitting diodes disposed in a matrix configuration, and the light-emitting diodes are lit when the first and second driving parts are driven simultaneously,
driving of at least one of the first and second driving parts is curtailed according to a predetermined operation mode.
A driving period of at least one of the first and second driving parts may be dynamically changed (period-2, shown in FIG. 2B) according to the predetermined operation mode. In the other words, a non-driving period (the period subsequent to the period-1, shown in FIG. 2B) of at least one of the first and second driving parts may be inserted.
A non-driving cycle (fifth cycle of each driving period in the example shown in FIG. 2C) in which at least one of the first and second driving parts is not driven may be inserted into a driving period of the first and second driving parts according to the predetermined operation mode.
An output time interval of at least one of the first and second driving parts may be changed/shortened according to the predetermined operation mode (as shown in FIG. 2D).
Thereby, it is possible to render power saving when an image forming apparatus or the like to which the display device according to the present invention is applied enters the predetermined mode (standby mode), without changing a basic program of the apparatus, by appropriately curtailing the driving of the LEDs. Furthermore, when the apparatus enters the standby mode, this matter can be clearly indicated to a user by changing the brightness of the LEDs.
Further, power consumption of the display device and the light emitting intensity of the LEDs in the standby mode can be freely set through control of the frequency of the curtailed driving, the ratio/rate of the non-driving cycle, or the driving time interval.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.